fix(linux): suppress benign GDK cursor theme and synthetic device log spam in Linux runner

[ZhuchkaTriplesix]

Problem

When running the Linux release binary, the terminal is flooded with repetitive GDK warnings during window dragging and mouse movement:

Gdk-Message: 21:23:25.829: Unable to load  from the cursor theme
(com.queryahub.querya_desktop:42717): Gdk-CRITICAL **: 21:23:28.135: gdk_device_get_source: assertion 'GDK_IS_DEVICE (device)' failed
(com.queryahub.querya_desktop:42717): Gdk-CRITICAL **: 21:23:30.007: gdk_device_get_source: assertion 'GDK_IS_DEVICE (device)' failed

Root Cause

1. gdk_device_get_source assertion: Triggered in GTK 3.24+ when bitsdojo_window / custom CSD window titlebar drag initiates pointer grabs or handles synthetic motion events where event->device is NULL.
2. cursor theme message: Triggered when Flutter's Linux engine passes an empty cursor name string ("") to gdk_cursor_new_from_name.

Proposed Solution

• In linux/runner/main.cc, install a GLib structured log writer filter via g_log_set_writer_func to suppress these benign GDK display/device assertions.
• Ensure all legitimate application crashes, exceptions, and non-GDK errors continue to be output to stderr.
• Verify clean terminal output when launching and interacting with Querya Desktop on Linux.